Helicopters are known comprising a fuselage; a main rotor fitted to the top of a central portion of the fuselage; and an antitorque tail rotor for counteracting the torque transmitted by the main rotor to the fuselage.
Articulated main rotors and/or antitorque rotors are also known.
Articulated rotors comprise a drive shaft that rotates about a first axis; a hub that rotates integrally with the drive shaft about the first axis; and a number of blades projecting from the hub along respective second axes radial with respect to the first axis.
Each blade can rotate with respect to the hub about the respective second axis to adjust its angle of attack with the airstream, and is free to oscillate about the hub about a respective third axis to perform a so-called flapping movement. More specifically, each third axis is crosswise to the first axis and to the second axis of the relative blade.
Each blade is free to oscillate with respect to the hub and the other blades about a respective fourth axis, parallel to the first axis, to perform a so-called “lead-lag movement”.
A need is felt to damp vibration induced by lead-lag motion of the blades, using damping devices whose damping action is affected as little as possible by centrifugal force, so they are effective over a wide range of blade rotation speeds about the first axis, and a wide range of damping device positions along the second axes of the relative blades.
A need is also felt within the industry to damp vibration induced by lead-lag motion of the blades, using damping devices as lightweight and compact as possible.
Finally, a need is felt to damp vibration induced by lead-lag motion of the blades, using damping devices that require no operating fluid, e.g. oil, to function correctly, so as to simplify damping device construction and maintenance.